Power modules for the control of electric motors are used in many ways, for example to control the speed and performance of the electric motors. They normally consist of a power unit which has a circuit arrangement with semiconductor components, in particular integrated circuits (ICs) as circuit breakers, their own housing and connections for the power supply, for outputs (output voltage) and inputs (controls). They also normally have a separate heat sink to which the power unit is fitted for heat dissipation purposes, of the circuit breakers especially, as well as a separate control unit for the control of the power unit. Evaluation of the output voltage from the power module is normally carried out by a separate processing unit.
In the manufacture of the power module the power unit is usually manufactured first as a standard sub-assembly wherein the semiconductor components for the circuit arrangement are fitted to a substrate. The substrate is then soldered onto a carrier plate and the housing and connections are then fitted. This power unit is then screwed to the separate heat sink by its carrier plate (usually via an interface such as a heat conducting paste) as a standard sub-assembly. The circuit arrangement for the control unit, which is fitted to a suitable substrate (e.g. a PCB) separately from the power unit, is connected to the power unit (normally with a screwed connection). Because of the need for rugged feed lines (due to the design) between power unit and voltage supply as well as between the power unit and the control unit an additional compensation unit is needed for EMC purposes with a great number of semiconductor elements (coils and capacitors). The heat sink itself often also has to be connected to another cooling unit (liquid cooler) to dissipate the heat.
This sort of power module construction brings with it the following disadvantages:
The thermal resistance is conditional upon the internal construction of the power unit (substrate, carrier plate), the interface between the power unit and the heat sink and the separately-mounted cooling unit, such that poor heat transfer takes place, particularly between the semiconductor components (circuit breakers) of the power unit and the heat sink. PA1 Due to the separate construction method of the individually-manufactured components and functional units of the power module and the necessary line connections between the functional units a greater surface area/volume and weight is required, which involves higher costs. PA1 An increased amount of circuitry (multiplicity of semiconductor components, surface area requirement, costs) is necessary for the compensation unit. PA1 The connection between the heat sink and the additional cooling unit is costly and can often only be achieved with poor thermal contact. PA1 The semiconductor components for the circuit arrangement of the power unit are fitted to a suitable substrate and this substrate is directly fitted onto a heat sink with an optimized surface made of a material with good heat-conducting properties and is connected to this by soldering (for example with soft solder). PA1 The heat sink is designed as an insert section and can be integrated directly into the (complete) cooling unit of the power module. PA1 The control unit is fitted on a carrier in parallel in a separate plane at a given distance from the substrate which carries the circuit arrangement of the power unit, wherein the semiconductor components of the control unit can be arranged on one or both sides of the carrier and make contact with the circuit arrangement of the power unit through vertically-arranged contact pins (connecting bars or ties). As an option, if the semiconductor components of the control unit are only fitted to the top side of the carrier, a metallic plate can be fitted to the underside of the carrier, which faces the substrate, as an additional carrier for the purposes of EMC screening and increasing the mechanical strength (for example for use in motor vehicles). PA1 In another plane in parallel to and at a given distance from the control unit carrier (above the carrier) or on the same level as the control unit further functional units can be provided to implement additional functions (for example current measurement and signal processing) PA1 Compact design with low surface area/volume requirement and low cost. PA1 An improvement in heat transfer between the semiconductor components of the power unit and the heat sink through direct cooling of the semiconductors and the integration of the heat sink into the cooling unit. PA1 An increase in the reliability and service life of the semiconductor components of the power unit and thereby the power module. PA1 Due to the symmetric and minimal lengths of the connecting lines only a minimum amount of circuitry is necessary for the compensation unit to correct leakage inductance.